Various types and configurations of prosthetic heart valves are used to replace diseased natural human heart valves. The actual shape and configuration of any particular prosthetic heart valve is dependent to some extent upon the valve being replaced (i.e., mitral valve, tricuspid valve, aortic valve, or pulmonary valve). In general, the prosthetic heart valve designs attempt to replicate the function of the valve being replaced and thus will include valve leaflet-like structures used with either bioprostheses or mechanical heart valve prostheses.
As used throughout this specification a “prosthetic heart valve” is intended to encompass bioprosthetic heart valves having leaflets made of a biological material (e.g., harvested porcine valve leaflets, or bovine or equine pericardial leaflets), along with synthetic leaflet materials or other materials. These bioprosthetic heart valves typically include a stent having a substantially circular base (or stent ring), around which an annular suture material is disposed for suturing the prosthesis to heart tissue. The stent further typically includes at least two, but typically three, support structures extending from the stent ring. These support structures are commonly referred to as stent posts or commissure posts. These posts typically are rigid yet somewhat flexible structures extending from the stent ring, which are covered by a cloth-like material similar to that of the annular suture material. The stent or commissure posts define the juncture between adjacent tissue or synthetic leaflets otherwise secured thereto. Examples of bioprosthetic heart valves are described in U.S. Pat. Nos. 4,106,129 (Carpentier et al.), and 5,037,434 (Lane), the entire disclosures of which are incorporated herein by reference. These disclosures describe a conventional configuration of three leaflets, with one leaflet disposed between each pair of stent or commissure posts. Regardless of whether a stent is provided, however, bioprosthetic heart valves are generally tubular so that when the leaflets are in an open position, an internal passage is defined through which blood can flow.
The bioprosthetic heart valves further typically include a sewing ring or suture ring that provides a means for fixing the prosthetic heart valve to the patient's native heart valve orifice tissue (e.g., native annulus or valvular rim) that is associated with the native heart valve being repaired or replaced. In particular, an exacting surgical implantation technique is traditionally employed whereby the heart is stopped (i.e., cardiopulmonary bypass) and opened, which is followed by surgical removal of damaged or diseased natural valve structure. A prosthetic heart valve can then be oriented within the native valvular area, with the sewing ring being seated against or at the native annulus or valvular rim. Sutures are then used to affix the sewing ring to the natural tissue. Obviously, the risks associated with this invasive type of surgery are numerous, particularly when cardiopulmonary bypass procedures are used.
A successfully implanted prosthetic heart valve will normally function without problems for many years. In certain instances, however, deficiencies may become evident shortly after implant or within a few years, particularly in younger patients. Common functional deficiencies include the calcification of the prosthetic heart valve leaflets, stenosis, and prosthetic heart valve insufficiency. Under these and other circumstances, the prosthetic heart valve does not function properly and conventionally requires surgical removal and replacement. Surgical removal of such a previously implanted prosthetic heart valve entails the same invasive surgical intervention described above, coupled with the need to remove the old prosthetic valve and implant a new prosthetic heart valve. In addition, the risk of mortality is often higher when performing a second surgery in the same area of the body, particularly when performing heart-related surgeries. Another disadvantage to this additional surgery is that the reopening of a sternotomy has been known to have a relatively high risk of causing an infection.
Thus, while these types of surgeries are well-accepted, the conventional surgical intervention described above is difficult to perform and can result in patient injury or more severe complications. In fact, due to physical weakness of a patient, implantation of a prosthetic heart valve via the conventional surgical technique may be considered too high-risk or contra-indicated for certain patients. Further, removal of a previously implanted prosthetic heart valve requires cutting of the sutures that secure the prosthesis to the native annulus/valvular rim, and attachment of a new sewing ring via stitching, which can further compromise the integrity of the valvular rim and lead to recovery complications, morbidity, and mortality.
Although not necessarily related to the specific prosthetic heart valve replacement concerns described above, efforts have also been made to devise a prosthetic heart valve capable of being delivered percutaneously via transcatheter implantation, thereby avoiding the complications and risks associated with conventional surgical intervention. For example, in U.S. Pat. No. 6,168,614 (Andersen et al.), a heart valve prosthesis is described for implantation in the body by use of a catheter. The valve prosthesis consists of a support structure with a tissue valve connected to it, whereby the support structure is delivered in a collapsed state through a blood vessel and secured to a desired valve location with the support structure in an expanded state.
Other percutaneously-delivered prosthetic heart valves have been suggested having a generally similar configuration, such as by Bonhoeffer, P. et al., “Transcatheter Implantation of a Bovine Valve in Pulmonary Position.” Circulation, 2002; 102:813-816, and by Cribier, A. et al. “Percutaneous Transcatheter Implantation of an Aortic Valve Prosthesis for Calcific Aortic Stenosis.” Circulation, 2002; 106:3006-3008, the disclosures of which are incorporated herein by reference. These techniques rely at least partially upon a frictional type of engagement between the expanded support structure and the native tissue to maintain a position of the delivered prosthesis, although the stents can also become at least partially embedded in the surrounding tissue in response to the radial force provided by the stent and any balloons used to expand the stent. Thus, with these transcatheter techniques, conventional sewing of the prosthetic heart valve to the patient's native tissue is not necessary. Similarly, in an article by Bonhoeffer, P. et al. titled “Percutaneous Insertion of the Pulmonary Valve.” J Am Coll Cardiol, 2002; 39:1664-1669, the disclosure of which is incorporated herein by reference, percutaneous delivery of a biological valve is described. The valve is sutured to an expandable stent within a previously implanted valved or non-valved conduit, or a previously implanted valve. Again, radial expansion of the secondary valve stent is used for placing and maintaining the replacement valve.
Devices and methods have more recently been developed for percutaneously replacing deficient, previously implanted prosthetic heart valves, which are described, for example, in U.S. Patent Publication No. 2006/0052867 (Revuelta et al.), the entire disclosure of which is incorporated herein by reference. Other transcatheter technologies for delivering replacement valves are described in PCT Application Nos. WO 2007/053243-A2, WO 2007/130537-A1, and WO 2007/081820-A1; United States Patent Application Publication Nos. 2005/0251251-A1, 2007/0043435-A1, and 2008/0004696-A1; and U.S. Pat. No. 7,195,641. However, a need exists for additional delivery systems, and related methods of implanting replacement heart valves, that are conducive to percutaneous delivery for replacing a deficient, previously implanted bioprosthetic heart valve.